This is a proposal to establish a core pharmacology laboratory in affiliation with a new AIDS Clinical Trial Unit (ACTU). The laboratory will participate in studies that require determination of drug (or drug metabolite) concentrations in conjunction with research protocols. Similar support will be made available to other ACTU's as needed. The proposed laboratory will analyze drugs currently used in the management of AIDS, experimental nucleoside analogs undergoing clinical trial, and drugs that may be of interest in the future. It will also be concerned with the development of new and/or improved assays, when satisfactory ones are unavailable. The core laboratory will also perform assays in support of various developmental research protocols that have been submitted separately in conjunction with the proposed ACTU. This will enable the investigators to control for pharmacokinetic variability in their studies of mechanisms of drug toxicity and resistance. The core laboratory will have the capacity to employ diverse state of the art technologies for drug analysis, but it is expected that HPLC and immunoassay will be the primary modalities. It will have sufficient versatility to respond to advances in the state of the art of pharmacotherapy for HIV infection and its complications.